1. The Field of the Invention
Embodiments of the invention relate to methods for manufacturing polymeric coatings for implantable medical devices. More particularly, embodiments of the invention relate to methods for manufacturing copolymers that include a 1-methyl-2-methoxyethyl moiety and methods for using the polymers on medical devices.
2. The Related Technology
Implantable medical devices, including stents, can be coated with polymers to give the implantable device beneficial properties when used in living tissue. Implant coatings, particularly stent coatings, typically need to simultaneously fulfill many criteria. Examples of desirable properties for implant coating properties include: adhesion to the implant (e.g., adhesion to stent struts) to prevent delamination; adequate elongation to accommodate implant deformation without buckling or cracking; sufficient hardness to withstand crimping operations without excessive damage; sterilizability; ability to control the release rate of a drug; biocompatibility including hemocompatibility and chronic vascular tissue compatibility; in the case of durable or permanent coatings, the polymer needs to be sufficiently biostable to avoid biocompatibility concerns; processability (e.g. production of stent coatings that are microns thick); reproducible and feasible polymer synthesis; and an adequately defined regulatory path.
Many methacrylate polymers exhibit several of the forgoing properties. However, most, if not all, methacrylate homopolymers lack a desired property or a combination of desired properties. For example, homopolymers of methyl methacrylate and ethyl methacrylate are too brittle. Homopolymers of n-butyl methacrylate (PBMA) are typically too hydrophobic for adequate drug elution (water absorption is only 0.4%).
Recently, efforts have been made to copolymerize methacrylate polymers with other monomers to achieve a copolymer that has the benefits of known methacrylate homopolymers and overcomes their deficiencies. The challenge with developing novel methacrylate copolymers has been achieving the desired mechanical properties while maintaining biocompatibility and useful drug permeability. Good biocompatibility is required for patient safety, device efficacy and for obtaining regulatory approval to use the polymer on an implantable medical device.